Sparrowhawk (oz9436)

About this Plan

Sparrowhawk (aka Sperwer). Rubber duration model.

Quote: "Duration plane designed by J Van Hattum. Full size plan given away free with the March 1939 Aeromodeller."

Scan from DBHL, cleanup by theshadow.

ref DBHL-6170.

Direct submission to Outerzone.

Update 18/01/2020: Added article, thanks to IanEaston.

Quote: "The Sparrowhawk. Begin by carefully studying the drawings, until you are sure that every detail is quite clear. Read the text through a couple of times, referring to the drawings, and get familiar with the sequence and methods of construction. Many a good job has been spoilt because someone started right off without studying the plans. Also see to it that all materials are on hand and all the tools complete before building is started; there is nothing so annoying than having to hold up a job that is shaping well just because one forgot to get an important piece of material.

The Fuselage: Pin the plan on a flat board. Take two of the 1/8 in square balsa spars, place them along the upper and lower curve of the fuselage side, and cut them approximately to the right length. The illustration shows how the assembly is done by means of small blocks of scrap wood, pinned or nailed to the board. Start by putting in just a few, and adding on where needed. It doesn't require many. Next, place small bits of greaseproof paper under all the places where the struts will have to be glued to the longerons. This prevents the joints becoming stuck to the wood.

Now, when the longerons follow the side view perfectly, you can start cutting the vertical struts and fitting them in place. First try the fit and cut the struts a little too large. Never pass one which is too small and does not take up a sliding fit, nor one that is too long and forces the longerons apart. When the struts are ready, dip the ends in cellulose glue and drop a little glue on the longeron as well. Fit the strut in place and leave undisturbed to dry. (A better method, but it takes more time: cover the ends of the struts and the longeron with a thin film of glue and leave to dry. When dry apply glue once more and fit the strut in place. This gives a better joint.)

When all the struts have been put in their proper places, cut the nose and tail pieces from 1/8 balsa sheet. Note that the grain runs vertically. This is not sound from a carpenter's point of view, as one should never glue grains at right angles. However, if the grain ran horizontally the wood would split after a had shock. And balsa absorbs so much glue that we are justified in adopting this method.

When one side is finished, leave it to dry thoroughly. Some glues dry more quickly than others, but all like to be given time. Therefore a few hours' rest is advisable. (Meanwhile one can start on the ribs). When making the second side, take great care to get it exactly like the first, or the fuselage will be twisted. Now for the assembly.

Take the two sides and run a little glue on the four corners of the bulkheads 4 and 5, as well as on the four horizontal struts, which have been measured up from the plan-view. Leave to dry, and then glue the struts all on one side. They will tend to fall over, but one should just hold them more or less vertical until the glue has set and become tough. Then apply glue to the four remaining ends, and the corresponding point so on the other side. Again hold the job in place. When the glue has set so that there is no more danger of the struts becoming detached, place the fuselage in the normal position on the board and start trueing up. Place a drawing office set-square against the sides to see that they stand perfectly vertically. Also check the plan to see that one side is not ahead of the other. Next stretch a couple of elastic bands over the sides, fastened to the board by means of pins. This will hold the sides in place. Do not tighten the bands too much or they will cause the whole job to collapse. Don't force - persuade.

After the sides have been thus connected, fit the struts of the other bulkheads, upper and lower at the same time. Measure the length from the plan view. Finally, fit the balsa nose and tail pieces. Now look carefully along the fuselage to see if it is straight. If the job has been carried out properly, all the struts should he parallel. In the case where it is badly twisted, the only thing to do is to cut out the offending strut or struts and correct the misake by refitting them properly.

The Wing: Begin by making two templates of 1/16 three-ply and of the form shown for the ribs 1-7. Take care over this job, as the shape of the actual ribs will depend upon the accuracy with which this is done. Cut out the templates and finish with sandpaper. Then trace twelve ribs on the 1/16 balsa, grouping them in such a way that the material is used most efficiently. Two ribs are made of 1/8 balsa. Cut out the ribs, taking care to keep beyond the outline. Finish the lower surface straight by means of sandpaper and clamp them together, the two templates on the outside. By stretching a strip of sandpaper over a block of wood and nailing it to the sides we can make a very useful tool for sanding down flat surfaces. With this the curved upper surface of the ribs is brought to exact similarity to the template..."

Supplementary file notes

Article.
Original Sperwer plan, 1936.

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